Electrical power sources and the devices powered by them are generally connected by cables which provide for current flow between the power source and the device to be powered. Modern electronic circuits are usually direct-current (“DC”) powered, and the DC power supply often includes voltage regulation circuitry to provide for stable supply voltage level(s). For reasons of convenience and for ease of regulatory approval, small alternating current (“AC”)-to-DC power supplies (“converters”) that reside at the wall power outlet (“wall converters”) have become increasingly popular over the past few decades. It is noted that the terms “converter,” “voltage converter,” “power converter,” and “adapter,” shall be synonymous as used herein. It is also noted that the principles illustrated using examples herein may apply equally to AC/DC converters and DC/DC converters.
FIG. 1 is a prior-art block diagram illustrating a power converter 110 and a device 115 powered by the converter 110. The power converter 110 may, but need not be, a wall adapter. The power converter 110 and the powered device 115 are connected by a cable 120. The cable 120 includes two or more conductors (e.g., the conductors 125 and 130). Two or more conductors 125 may be necessary in the case of a multi-voltage power converter. The conductor(s) 125 carry current 135 to the powered device 115 and the conductor 130 carries return current 140.
There is a resistance 145 associated with the conductor 125 and a resistance 150 associated with the conductor 130. The values of both resistances 145 and 150 are a function of the gauge, length, and composition of the conductors 125 and 130, respectively. Currents 135 and 140 flowing through the resistances 145 and 150, respectively, cause a voltage drop across the cable 120 proportional to the currents 135 and 140. The cable voltage drop results in the input voltage V_PD 160 to the powered device 115 being unequal to the regulated output voltage V_OUT 165 of the converter 110. The cable voltage drop may be compensated for if the cable resistance characteristics and powered device operating currents are known by the designers of the converter 110.
An increasingly popular type of AC/DC converter supplies a regulated universal serial bus (“USB”) level voltage of 5.0 vdc for charging of mobile phones and other portable electronic devices. Such examples of the powered device 115 employ increasingly faster and more powerful processors, larger-capacity memory devices, etc., resulting in high current draws. The latter high current draws can result in a cable voltage drop that is significant in relation to a USB-level V_OUT 165 of 5.0 vdc. This situation can result in a challenge for cable voltage drop compensation at the regulation circuitry of the converter 110.